Q-jet power piston stop screw
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Instructor
Joined: May 2004
Posts: 134
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From: Central Wa
Q-jet power piston stop screw
In the process of rebuilding my Q-jet I removed the power piston stop screw and fogot to count the turns. I reinstalled it to the height I remember seeing. Is there a predetermined height or number of turns from the bottom. What are the effects if it is to lean or rich. I have a stock 1976 (except for true duals) with L48 4-spd. Compression is good, new timing chain and distributor. Timing is set at 9 deg and idle at 650 rpm. It seems to idle well and runs well but does smell rich while idling. I have set the idle mixture screws as lean as I can while maintaing a smooth idle. Spark plug color looks good as well.
Thanks
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From: St. Charles IL
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From: At my Bar drinking and wrenching in Lafayette Colorado
Here's the easy way to get it in the ballpark:
With the airhorn ("top") removed off the carb, depress the power piston until it seats. Observe the relationship between the top lip of the plastic retaining collar and the top of the piston brass sleeve (where the two hanger arms are pressed in). The top of the brass sleeve should protrude about .020" above the top lip of the plastic collar. Adjust to achieve this.
Once you have set this, knock the aluminum adjustment plug out of the airhorn before you install it. This will allow you to use a pair of skinny long-nosed needle pliers to grab and turn the piston adjustment screw from outside the carb. If the car feels sluggish and lean when test driving it, give the screw a 1/2 turn adjustment counter clockwise (raising the piston). If it seems too rich (as indicated by the idle mixture screws producing best idle at a setting of less than 4 turns out from seated), run the piston down 1/2 turn.
Lars
With the airhorn ("top") removed off the carb, depress the power piston until it seats. Observe the relationship between the top lip of the plastic retaining collar and the top of the piston brass sleeve (where the two hanger arms are pressed in). The top of the brass sleeve should protrude about .020" above the top lip of the plastic collar. Adjust to achieve this.
Once you have set this, knock the aluminum adjustment plug out of the airhorn before you install it. This will allow you to use a pair of skinny long-nosed needle pliers to grab and turn the piston adjustment screw from outside the carb. If the car feels sluggish and lean when test driving it, give the screw a 1/2 turn adjustment counter clockwise (raising the piston). If it seems too rich (as indicated by the idle mixture screws producing best idle at a setting of less than 4 turns out from seated), run the piston down 1/2 turn.
Lars
